Systolic spike on transcranial Doppler ultrasound in brain death determination: a matter of numbers

Dear Editor, We read the review by Corrêa et al. with interest: it is a precise overview of the role imaging plays in the determination of brain death prior to defi nitive clinical examination. Furthermore, it reviews several methodologies to identify cerebral circulatory arrest. Noteworthy are the data on transcranial Doppler ultrasound, a noninvasive technique which requires no contrast media, as well as being reproducible, inexpensive, and user-friendly, even at the bedside. However, we fi nd the defi nition of “systolic spike” misleading as it is reported as “short (< 100 cm/s) spikes in the early systolic phase with no fl ow in the remaining cardiac cycle”. Our considerations are as follows. Characteristic changes are involved in the development of cerebral circulatory arrest involving the wave form velocity of the basal cerebral arteries. Different steps can be identifi ed. 1. A rise in intracranial pressure. When the intracranial pressure (ICP) is normal, there is a single-phase fl ow in systole and diastole toward the brain in the spectra. When ICP increases, there is a reduction in end-diastolic velocity (EDV). Once the ICP reaches diastolic blood pressure, EDV becomes zero. When the ICP is above diastolic blood pressure, the brain receives blood only in systole, during which the systolic fl ow observed on a sonogram is known as the “systolic peak”. Because the cerebral perfusion pressure is still higher than the ICP, there is still a clear forward fl ow. 2. Oscillating fl ow. ICP increases continuously, and systolic peak duration is even shorter, thereafter, the diastolic fl ow is reversed. When the spectra is characterized by systolic forward and diastolic backward fl ows, the sonogram is said to show “oscillating fl ow” or a “to-and-fro” pattern. That means that the forward net current is zero, the ICP has exceeded the cerebral perfusion pressure, and the cerebral circulation has stopped. 3. Systolic spikes. As the ICP continues to increase, approaching the systolic blood pressure, the diastolic reverse current disappears, and isolated “systolic spikes” appear in the spectra. Systolic spikes must present a systolic peak of < 50 cm/s, rather than 100 cm/s, and a duration of < 200 ms, rather than 100 ms. 4. Lack of signal. With a very high ICP, the systolic spike amplitudes gradually decrease and in complete cessation of blood fl ow the signal cannot be observed. The adoption of this pattern in the diagnosis of cerebral circulatory arrest is controversial, because the lack of acoustic signal may be secondary to an inappropriate (overly thick) transtemporal window. However, identifi cation of the fl ow is a must prior to the fl ow arrest condition. In conclusion, the specifi c spectra observed in cerebral circulatory arrest are oscillating fl ow, systolic spike, and signal absence on the sonogram. In the end, the defi nition of systolic spike is a matter of numbers (milliseconds). REFERENCES


Dear Editor,
We read the review by Corrêa et al. (1) with interest: it is a precise overview of the role imaging plays in the determination of brain death prior to defi nitive clinical examination. Furthermore, it reviews several methodologies to identify cerebral circulatory arrest. Noteworthy are the data on transcranial Doppler ultrasound, a noninvasive technique which requires no contrast media, as well as being reproducible, inexpensive, and user-friendly, even at the bedside. However, we fi nd the defi nition of "systolic spike" misleading as it is reported as "short (< 100 cm/s) spikes in the early systolic phase with no fl ow in the remaining cardiac cycle". Our considerations are as follows.
Characteristic changes are involved in the development of cerebral circulatory arrest involving the wave form velocity of the basal cerebral arteries (2) . Different steps can be identifi ed.
1. A rise in intracranial pressure. When the intracranial pressure (ICP) is normal, there is a single-phase fl ow in systole and diastole toward the brain in the spectra. When ICP increases, there is a reduction in end-diastolic velocity (EDV). Once the ICP reaches diastolic blood pressure, EDV becomes zero. When the ICP is above diastolic blood pressure, the brain receives blood only in systole, during which the systolic fl ow observed on a sonogram is known as the "systolic peak". Because the cerebral perfusion pressure is still higher than the ICP, there is still a clear forward fl ow.
2. Oscillating fl ow. ICP increases continuously, and systolic peak duration is even shorter, thereafter, the diastolic fl ow is reversed. When the spectra is characterized by systolic forward and diastolic backward fl ows, the sonogram is said to show "oscillating fl ow" or a "to-and-fro" pattern. That means that the forward net current is zero, the ICP has exceeded the cerebral perfusion pressure, and the cerebral circulation has stopped.
3. Systolic spikes. As the ICP continues to increase, approaching the systolic blood pressure, the diastolic reverse current disappears, and isolated "systolic spikes" appear in the spectra. Systolic spikes must present a systolic peak of < 50 cm/s, rather than 100 cm/s, and a duration of < 200 ms (3) , rather than 100 ms.
4. Lack of signal. With a very high ICP, the systolic spike amplitudes gradually decrease and in complete cessation of blood fl ow the signal cannot be observed. The adoption of this pattern in the diagnosis of cerebral circulatory arrest is controversial, because the lack of acoustic signal may be secondary to an inappropriate (overly thick) transtemporal window. However, identifi cation of the fl ow is a must prior to the fl ow arrest condition (4) .
In conclusion, the specifi c spectra observed in cerebral circulatory arrest are oscillating fl ow, systolic spike, and signal absence on the sonogram. In the end, the defi nition of systolic spike is a matter of numbers (milliseconds).

Dear Editor,
We thank Morelli et al. for their interest in our paper on the role of neuroimaging in the determination of brain death, as well as for their comments on the transcranial Doppler ultrasound features of brain death, since this allows a more indepth debate on the topic. After carefully reading the letter, we understand that the authors concerns are based on the numeric values of the systolic spike pattern, considering the peak velocity at the beginning of systole as well as the duration of this peak. The aim of our article was to review the key neuroimaging features of brain death, with emphasis on computed http://dx.doi.org/10.1590/0100-3984.2022.0125 Radiol Bras. 2023 Jan/Fev;56(1):50-51 tomography and magnetic resonance imaging. Because these methods are not considered as ancillary tests in the determination of brain death, they are often disregarded in the assessment of such. Therefore, we did not delve into the technical details and controversies of the other imaging methods.
However, we included all of the neuroimaging examinations considered as ancillary tests for brain death determination in Brazilian Federal Council of Medicine Resolution 2.173, including transcranial Doppler ultrasound. According to the 2014 "Latin American consensus on the use of transcranial Doppler in the diagnosis of brain death" (1) , systolic spikes are "very short sonograms with a duration of less than 200 ms, appearing at the beginning of the systolic phase without a flow signal in the remainder of the cycle, and a systolic velocity ≤ 100 cm/s" (1) , as we considered in the article. Hassler et al. (2) also described the systolic spike pattern as being characterized by a sharp narrow peak at the beginning of systole, with a maximum flow velocity of up to 100 cm/s. Nevertheless, we recognize that other studies, including the "Brazilian guidelines for the application of transcranial ultrasound as a diagnostic test for the confirmation of brain death" (3) , which was published in 2012, define short systolic peaks as those with a peak velocity of less than 50 cm/s (3,4) .
In conclusion, we agree with Morelli et al. that the definition of systolic spike on transcranial Doppler ultrasound in brain death is a matter of numbers. Systolic spikes appear at the beginning of the systolic phase without a flow signal in the remainder of the cycle, with a duration of less than 200 ms and a low systolic peak velocity. Some authors define low systolic peak velocity as less than 100 cm/s, whereas others define it as less than 50 cm/s.